Leveling control system for road building machines



1964 R. A. GURRIES ETAL 3, 0

LEVELING CONTROL SYSTEM FOR ROAD BUILDING MACHINES Filed May 9, 1961 2Sheets-Sheet 1 IN VEN TOR! 84 YMONO A. 6029/55 JOHN a/fltrr Nov. 3, 1964R. A. GURRIES ETAL 3, 55,0 0

LEVELING CONTROL SYSTEM FOR ROAD BUILDING MACHINES Filed May 9, 1961 2Sheets-Sheet 2 INV EN TOR! 247M040 4. 61/99/55 Jam awn-r7 arrow i3,155,620 LEVELWG CQNTRUL SYTEM FOR RQAD BUILDZNG MACHlNES liiayinondA.Quarries, San dose, and .llohn Curlett, Los Gatos, Calih, assignors toQuarries Manufacturing Co., an Jose, Calif, a corporntionof CaliforniaFiled May 9, 1961, Ser. No. 108,902 Galina. (Ql, 94-419) This inventionrelates to road building machines and more particularly to a grade-wirehanger and a wire fork centering support used in connection withleveling control systems for road building machines.

Practically all road building machines comprise: A plurality of tractionunits engaging the ground for supporting and moving the road buildingmachine; one or more road building tools such as striker blades,scrapers, conveyor screws, hoppers; and support means connecting theroadbuilding tools to the traction units. ince the traction units are indirect contact with the ground where grade, cross grade and generalsurface conditions are usually different from the road surface level tobe constructed, it is essential that the support means provide forvertical adjustment between the road building tools and the tractionunits to permit the maintaining of the position of the road buildingtool at an accurate and predetermined level reflecting a desired gradeand cross grade irrespective of the grade, cross grade andirregularities of the ground en aged by the traction unit.

Supports, which provide for vertical adjustment of the road buildingtool, conventionally may include, for example, valve operated hydraulicrams, solenoid actuated motorized worm and pinion or cam and camfollower combinations as Well known to those skilled in the art. Thevalves or solenoids or other control means are actuated whenever theroad building tool deviates from the desired height, grade and crossgrade. Conventionally, the control means for actuating the individualsupports include horizontally disposed wire forks mounted to the roadbuilding tool or the frame carrying the tool and which engages, instraddle fashion, a tautly strung grade-wire supported at the desiredgrade along the side of the road in wire hangers mounted upon stakesanchored into the ground. The wire fork traces the wire and anydeviation of the angular position of the fork from a predeterminedangular position (usually horizontal) constitutes an error signal whichis utilized to actuate the supports and thereby the vertical height ofthe tool-to bring the wire fork back to its predetermined angularposition. The wire fork may be connected to a shaft which eitherdirectly or through a suitable mechanical linkage actuates the hydraulicvalves or solenoids or may be pivotally mounted to close and open microswitches which operate the hydraulic valves or solenoids as is wellknown.

The wire hangers of the prior art devices presented a blocking obstacleto the smooth flow of the wire tracing wire fork requiring the Wire forkto swivel out of the path of the wire hanger to clear it. For thisreason the wire fork was swivelly mounted upon a vertical axis andincluded a spring centering means to restore the wire fork to itscontrol position after the obstacle had been cleared. During theinstance of time when the wire fork was swiveled back, the levelingcontrol was temporarily interrupted, at least to a certain degree.Positive control was restored when the wire hanger was cleared and thewire fork jumped back to its central position. In case of great roadirregularity, the wire fork often completely disengages itself fromthegrade wire in its swiveled back position requiring stoppage of theroad building machine until the fork Was once more engaging thegrade-wire.

atent Also the constant swiveling action puts severe stress upon thespring centering means necessitating its frequent re placement.

It is therefore an object of this invention to provide a wire fork andwire hanger combination in which the wire fork can smoothly pass overthe wire hanger remaining at all times centered on the grade-wire in itstransversely extended position.

It is a further object of this invention to provide an improved wirefork centering means which is more rugged, reliable and economical thanthose used heretofore.

It is still another object of this invention to provide a wire hanger ofa novel configuration which permits the wire fork to gradually spreadits prongs upon encountering the hanger to clear it and which supportsthe gradewire so that the spreading wire fork is always centered on thegrade-wire.

It is still a further object of this invention to provide a Wire hangerof novel configuration and a wire fork centering means to keep the wirefork in engagement with the grade-wire to thereby insure smoothoperation and constant control of the leveling system.

in accordance with a preferred embodiment of this invention, the wirehanger includes a fork spreading plate mounted at right angles to thewire carrying end of the wire hanger. The vertical dimension of the forkspreading plate decreases from its mid-portion in both directionsthereby following the shape of an oval. The plate also has narrow endportions to permit the prongs of the wire fork to engage oppositesurfaces of the plate and to spread slowly over both sides thereof, andafter passing to return to their normal contracted position. The wireruns behind the plate and centrally with respect thereto so that thewire fork is always centered on the grade-wire. inorder to permit thewire fork to spread around the wire hanger rather than to pivot awayfrom it, a firm flexible support is provided which keeps the feeler forkin its outwardly extended position unless the obstacle encountered bythe far end of the wire fork is greater than the spreading actionnecessary to negotiate the plate.

Other objects and a better understanding of this invention may be had byreference to the following specifications and appended claims and thedrawings in which:

FEGURE 1 shows a side view of the wire hanger and the wire fork of thisinvention in which the wire fork is pivotally supported by the roadbuilding machine and ctuates the supports by translational motion;

FIGURE 2 shows an enlarged top view of the wire fork of this inventionin which the wire fork is connected to a shaft and actuates the supportsthrough rotation of that support shaft;

FIGURE 3 shows an enlarged front view of the fork shield of the wirehanger;

FIGURE 4 shows a side view of the fork shield of FKGURE 3, together withthe engaging prong portions of the wire fork; and

FTGURE 5 shows, in perspective view, the wire hanger mounted upon aground stake and several progressive stages of prong engagement andprong spreading of the wire fork upon straddling the fork shield.

Referring now to the drawin s, in which like reference charactersdesignate like parts, there is shown in FIGURE 1 a stake ll) which maybe made of steel having a circular cross section and which supports awire hanger l2 having a boss 14- with an Opening dimensioned for slidingengagement with stake it). Boss 14 is provided with an end boss 16having a threaded hole to accommodate set screw 13. Set screw 1% istightened against stake it? to secure wire hanger i2 thereto. Wirehanger 12 includes a short slot 2% (FIGURE 4) for accommodating gradewire 21 and a fork spreading plate 2.2, an enlarged view of which isshown in FIGURE 3. A wire fork 24 shown in engagement with the wire 21has its inner closed end supportably inserted into a swivelable sleeve26 and is fastened thereto by a retainer key 28 held in place by a setscrew 36 so that its prongs 95 and 96 lie in a vertical plane. Spacerpin 32 abuts the closed end of wire fork 2d and prevents it from slidinginwards into sleeve 26.

Sue end of sleeve 26 is provided with a cylindrical boss 34 which isrotatably supported about a pin 36 in a forked bracket 38 permittingsleeve 26 to pivot in a horizontal plane. Clamped to one prong of forkedbracket 38 is a forked support 4t) which has welded or otherwise firmlyattached thereto one end of a closely wound extension spring 42 forcentering sleeve 26. The other end of extension spring 42 is rigidlyconnected to a centering shaft 44 which rides in a hole 58 contained ina centering brace 46 welded to or otherwise afiixed to sleeve 26. Tofacilitate the insertion of centering shaft 44 into hole 48, forkedsupport dtl is held in place by a screw ll which permits its removalfrom bracket 38.

Forked bracket 38 is suitably fastened to a cylindrical hub do which ispivotably mounted upon a pivot shaft 32. Pivot shaft 32 is connected tothe tool or tool carrying portion of the road building machine (notshown) in such a way that its axis is parallel to the normal directionof motion of the road building machine. An arm 84 is affixed to hub 8ft,preferably but not necessarily axially with and diametrically opposed tosleeve 26, to which some means, illustrated schematically as a lever 35,is attached which communicates with a support actuating mechanism 86.Support actuating mechanism forms no part of this invention and maycomprise, as already stated, mechanical or electrical actuating membersconnected, either directly or indirectly, to hydraulic valves orelectrical solenoids or switches which actuate the supports. Acounterweight '73 may be slidably supported by arm 84 to provide balanceabout pin 32.

Referring now to FTGURE 2, there is shown the same wire fork as inFIGURE 1 supported by forked bracket 38 but instead of connectingbracket 38 to a pivotable hub and operating the actuating mechanism bylever 85 connected to arm 84, bracket 3% is connected to a hub which iseither directly or indirectly (as illustrated) mounted upon a rotatableshaft 66 which operates a support actuating mechanism 56. Supportactuating mechanism 56 just as mechanism 86 forms no part of thisinvention and may comprise, as previously stated, mechanical orelectrical actuating members connected either directly or indirectly tothe means in the supports which provide the vertical adjustment.

Hub 5t), as stated, may be directly connected to shaft 66 which justlike pivot shaft 32 is connected to the tool or tool carrying frame ofthe road building machine and which has its axis parallel to the side ofthe road building machine. If directly connected to shaft 66, hub 59comprises a cylindrical sleeve having an inner bore dimensioned forengagement with shaft 66 and including some means for firmly fasteningit to shaft es. Such means may comprise a set screw through one side ofhub Sti, a key accommodated in a key way or other suitable means.

In some applications, where the angular deviation of shaft 66 is to belimited to a maximum value, hub 50 may be provided with an angularoverload assembly generally designated by reference character 54-.Angular overload assembly 54 is fully described in a copendingapplication, Serial No. 862,276, filed December 28, 1959. Briefly,assembly 54 comprises hub 50 rotatably mounted about a spindle dtlhaving a flange 62 and a cylindrical bore 64- dimensioned for engagementwith shaft 66. Another flange 63 of substantially the same configurationas flange 62 is mounted upon the lower end of spindle dd. Shaft 66passes through cylindrical bore 64 and is conventionally secured tospindle es. Between hub Bill and flanges 62 and 6? respectively, twoaxially spaced circular chambers 67 and 69 are formed for accommodatinga pair of torsion springs 7d and 71. Torsion springs id and '71 havetheir respective ends tied to hub 5t and flanges 62, 63. As long as thechange in angular position of sleeve 26 about shaft 66 is smaller thanmaximum amount, angular overload assembly 54 through torsion springs 7and 71 make spindle dd follow hub 5t). if the change in angular positionis greater than the maximum displacement permitted shaft 66, hub 5t putstorsion springs '71 and 71 under torsion and spindle dd is not forcedpast the maximum allowable angular displacement of shaft 66.

Hub 5t? may be provided with a counterweight '73 adjustably mounted onan arm 72 to counteract the torque on hub 5% due to the weight of sleeve26, wire fork 2d and spring 42.

Referring now to FIGURE 3, fork spreading plate 22 is provided with adiagonally extending slot which either communicates directly with shortslot 263 holding grade wire 21 in its horizontal position or whichextends past plate 22 and actually forms short slot 2h. The angle formedbetween slot 9% and wire 21 is illustrated as being about 30 degrees sothat grade-wire 21 need not be unnecessarily stretched when inserted andonce inserted will be secure in slot 2th against inadvertentdislodgement. The width of the slot is preferably considerably widerthan the grade-wire so that if slot 2d is formed by extending slot 9tpast plate 22, grade-wire 21 may lie horizontally despite the diagonalinclination of the slot. The contour of fork spreading plate 22comprises two substantially identical arcuate surfaces 92 and 9dintersecting in two places to form edges 97 and 98. The particularcurvature of arcuate surfaces 92 and M is not very important-they may becircular, parabolic, oval or elliptical. What is important is that thevertical distance between surfaces 92 and 94 increases gradually fromedge i7 to a maximum and then decreases gradually towards edge 98.Additionally, surfaces 92, and 9d are symmetric about grade wire Zll sothat the vertical distances from either surface to wire 21 is the same.Fork spreading plate 22 may be cast as an integral part of wire hanger12, or may be a separately manufactured plate bolted thereto.

FIGURE 3 also shows three progressive positions assumed by prongs 95 and95 of wire fork 2 passing over fork spreading plate 22.. Prior toengagement with fork spreading plate 22, prongs Sa and 96a straddle wire21 moving from right to left towards edge 9%. Thereafter prongs 95 andas start sliding over surfaces 92 and )4 until spread apart a maximumamount indicated by posi tions 95!; and 965. From that position onward,the spreading again decreases and near edge 98 the prongs are again incontact with grade-wire 211. as shown by prong positions 950 and 960.

FIGURE 4 shows fork spreading plate 22 and wire hanger 12 as one castpiece in which short slot 2% which may be the extension of diagonal slotW as previously stated, holds grade-wire 21. The depth of short slot 2tneed only be such that grade-wire 21 may assume its horizontal positionthat it may clear fork spreading plate 2d. Further, prongs 95 and 96have their ends bent away from one another to form a V portion whichfacilitates engaging wire fork 24- with grade-wire Zll.

In operation, the end of wire fork 24 traces grade-wire 21 and sincefork 24 is tangularly supported either about pivot shaft 82. or aboutconnecting shaft 66 the angular position of fork 24 will change wheneverthe tool or tool carrying frame height differs from the desired heightas set by the grade-wire. In case of the pivot mounting illustrated inFIGURE 1, lever fastened to arm 34 will initiate corrective action torestore the tool height to its proper height. In case of the shaftconnected mounting illustrated in FIGURE 2, rotation of shaft 66 willactuate mechanism 56 to restore the tool to its proper height.

As the road building machine moves along grade-wire 21, wire fork 24remains in engagement with grade-wire El and upon encountering wirehanger 312, its prongs and 96 are spread apart to move smoothly oversurfaces 92 and 94 of fork spreading plate 22 as shown in FIG- URE 5.Since, as has been previously stated, surfaces 92i-and 94 areequidistant from gradewire 21, wire fork remains centered on andcontinues to trace grade-wire 21 during its contact with spreading plate22 assuring constant leveling control at all times.

There may be instances when the road building machine moves closer tostake 14? than is shown in FIGURE 1 so that Wire fork 24 hits stake It).In order to avoid bending of prongs 95 and 96 and undue strain on theboom, sleeve 26 is mounted so it can pivot about a vertical axis throughpin 36 and thereby yield to an insurmountable obstacle. Spring 42 keepssleeve 26 yieldably centered permitting pivoting when fork 24 encountersa large obstacle and restore sleeve 26 to its central positionimmediately upon passing the obstacle.

FIGURE 2 shows sleeve 26' deflected about the center line of pin 36 andthe bending of centering spring 42, which provides the restoring torqueto bring it b ack to its normal position.

Spring 42 provides sufficient centering force to sleeve 26 so that wirefork 24 upon enocountering an obstacle such as thickening plate 22,sleeve 26 remains centered allowing fork 24 to spread its prongs overplate 22. On the other hand, spring 42 does not provide sufficientcentering force to permit the bending of fork 24. Furthermore, spring 42is closely wound to provide some damping about the center position ofsleeve 26 so that after being released from its pivoted position is willnot oscillate to any appreciable degree. This damping is an inherentproperty of closely wound spring :and is due to the fact that the coilson the side of greatest curvature are closely adjacent while springaction is provided by the coil separation on the side of smallestcurvature. As one end of the closely wound coil is moved back and forthfrom normal position, a restoring force is provided by the side of thespring on which the coils separate due to spring deformation. The otherside of the coil does not contribute a restoring force since there is nochange, such as contraction or separation, in the individual coils. Asthe coil passes through its normal position, the action of the coilsides are exchanged. As a consequence of such an exchange of sidesproviding the restoring force, such a spring includes damping and doesnot cause the horizontal boom to oscillate.

counterweight 73 is adjusted so that when fork 24 is not engaging wire21, sleeve 26 remains horizontal. The reason for balancing arm 26 is toavoid putting a tooheavy weight on the grade-wire 21, necessitatingclose spaced support to prevent it from sagging. The more evenly arm 26is balanced, the greater may be the separation between adjacent stakessince the grade wire need not support arm 26.

There has been described a wire fork centering means and a wire hangerwhich permits the Wire fork to spread over the wire hanger and remaincentered on the gradewire when passing a wire hanger. Under ordinaryoperating conditions, the boom may remain horizontally extended whenpassing the wire hangers providing continuous tracing and therebypositive leveling control and is not subjected to the punishment ofbeing constantly forced to yield.

What is claimed is:

1. In a road building machine in which the height of the road buildingtool is maintained in relation to the height of a ground supportedgrade-wire extending along the path of movement of said road buildingmachine, and in which road building tool actuating mechanisms areprovided for raising and lowering said tool, a height control systemcomprising: a fork assembly support pivotably mounted to said roadbuilding machine for movement in a plane perpendicular to the machinepath of movement, a horizontally extending fork assembly horizontallypivotably connected to said support, a closely wound extension coilspring connected between said support and said fork assembly, a pair ofspreadable prongs extending from said fork assembly; a plurality ofstakes; a wire hanger connected to each stake, said Wire hangerincluding a short slot for supporting said grade-wire and a forkspreading plate at the open end of said short slot, said fork spreadingplate having a diagonally extending slot communicating with said shortslot and having a vertical dimension centered about said short slotwhich gradually diminishes along a horizontal direction away from bothsides of said short slot, said wire fork being adapted to embrace andslide along said grade wire and said coil spring providing asufficiently stiff centering support to resist'horizontal movement ofsaid fork assembly upon engagement with a fork spreading plate to causesaid prongs to spread over said fork spreading plate, and meansresponsive to the pivotable motion of said support in said perpendicularplane and operative to actuate said tool actuating mechamsm.

2. In a road building machine in which the height of the road buildingtool is maintained in relation to the height of a ground supported gradewire extending along the path of movement of said road building machineby a control actuating assembly, said assembly comprising: height meansfor changing the vertical height of said road building tool; a fork.assembly support; means for pivotably supporting said fork assemblysupport for movement in a plane perpendicular to machine path ofmovement; a fork assembly swivelably connected to said support forswiveling in a horizontal plane a closely wound extension coil springconnected between said fork assembly support and said fork assembly tokeep said fork assembly normally in a predetermined angular dispositionin a plane parallel to machine path of movement, a pair of spreadableprongs extending from said fork assembly operative to engage saidgrade-wire; a plurality of stakes; and a wire hanger connected to eachstake, said wire hanger including a short slot for supporting saidgrade-wire; a fork spreading plate at the open end of said short slot,said fork spreading plate having a diagonally extending slotcommunicating with said short slot, the vertical dimension of said forkspreading plate being defined by concavely opposed and intersectingsurfaces decreasing in separation toward the point of intersection, saidcoil spring providing a sufficiently stiff centering support for saidfork assembly to resist movement of the latter from said predetermineddisposition so that engagement of said fork with said fork spreadingplate causes said prongs to slide over said concavely opposed surfacesand spread, and means responsive to the angular position of said supportin said perpendicular plane for actuating said height means.

3. A level control assembly for road building machines in which theheight of the road building tool is maintained by a tool height controlmeans in relation to the height of a ground supported grade-wireextending along the path of movement of said road building machinecomprising: a control member mounted to said road building machine forlimited angular displacement about a horizontal axis, said controlmember being operative to actuate said tool height control means inresponse to its angular position in a plane perpendicular to machinepath of movement; a fork assembly support mounted to said controlmember; a fork assembly pivotably connected to said support; a closelywound extension coil spring connected between said support and said forkassembly; a pair of spreadable prongs extending from said fork assembly;a plurality of stakes; and a wire hanger connected to each stake, saidwire hanger including a short slot for supporting said grade-wire and afork spreading plate at the open end of said short slot, said forkspreading plate having a diagonally extending slot communicating withsaid short slot and having a vertical dimension centered about saidshort slot which gradually decreases with increased horizontal distancefrom said short slot, said wire fork being in engagement with said gradewire and said coil spring centering said fork assembly with respect tosaid control shaft and providing sufficient centering force to hold saidfork against horizontal displacement and cause said prongs to spreadover said fork spreading plate when moved into engagement therewith.

4. A wire fork assembly for controlling the vertical tool height of aroad building machine in accordance with a ground supported grade-wireextending along the path of movement of said road building machine, saidWire fork assembly comprising: a control member rotatably mounted tosaid road building machine for limited angular displacement about anaxis parallel to said grade wire, said control member being operative toactuate control means for selectively raising and lowering said verticaltool height in response to an angular position about said axis; a sleevesupport mounted to said control shaft, a horizontally extending sleeveswivelly connected to said sleeve support for swiveling about a verticalaxis; a closely wound extension coil spring connected between saidsleeve support and said sleeve for normally centering said sleeve aboutan axis perpendicular to said control member; and a wire fork supportedby said sleeve and operative to engage said grade wire.

5. A wire fork assembly and leveling means for maintaining the verticaltool height of a road building machine in relation to a ground supportedgrade-wire extending along the path of movement of said road buildingmachine, said wire fork assembly comprising: a control shaft rotatablymounted to said road building machine for angular displacement about anhorizontal axis, said control shaft being operative to actuate a controlmeans for selective raising and lowering said road building machine inresponse to an angular position in a vertical plane; a sleeve supportmounted to said control shaft; a horizontally extending sleeve swivellyconnected to said sleeve support for swiveling about a vertical axis; aclosely wound extension coil spring having an axis normally extendingperpendicularly to said control shaft and intersecting said verticalaxis, opposite ends of said spring being respectively connected to saidsleeve support and said sleeve to resiliently support said sleeve in acentral position; and a Wire fork held by said sleeve and engaging saidgrade-wire.

6. A wire fork assembly operative to actuating a level control means formaintaining the vertical tool height of a road building machine inrelation to a ground supported grade-wire extending along the path ofmovement of said road building machine, said wire fork assemblycomprising: a support pivotably mounted to said road building machine; ahorizontally extending sleeve swivelly connected to said support forswiveling about a vertical axis; a retaining plate connected to saidsleeve; a closely wound extension coil spring normally extendingperpendicularly to said control shaft and whose axis intersects saidvertical axis, one end of said spring being fixed to said sleeve supportand the other end of said spring being in engagement with said retainingplate; and a wire fork having one end supported in said sleeve and itsother end in engagement with said grade-wire to pivot in a verticalplane about said support mounting in response to variations in toolheight relative to said grade-wire.

7. A support for a grade-wire adapted to be extended along the path ofmovement of a road building machine so that the grade-wire may beengaged by a Wire fork mounted to said road building machine, saidsupport comprising: a stake; and a wire hanger having one end thereofadjustably connected to said stake, the other end of said wire hangerincluding a short slot and a vertically extending fork spreading platehaving a diagonally positioned slot extending there through andcommunicating with said short slot, the vertical dimension of said forkspreading plate b ng defined by two smooth arcuate coneavely opposedsurfaces intersecting at edges lying in a horizontal plane atsubstantially the level of said short slot.

8. A support for a grade-wire adapted to be extended along the path ofmovement of a road building machine, said support being adapted topermit smooth uninterrupted engagement of a wire fork mounted to saidroad building machine with said grade wire, said support comprising: aground support stake and a wire hanger having one end thereof adjustablyconnected to said stake, the other end of said wire hanger including avertically extending fork spreading plate having a diagonally positionedslot extending there through and into said wire hanger, portions of saidslot being conditioned to support and retain a grade-wire, said forkspreading plate having two concavely opposed surfaces intersecting in ahorizontal plane containing said slot portions, said opposed surfacesbeing operative to gently force apart the prongs of a wire fork movinalong a grade-wire into engagement with said surfaces to permit saidwire fork to remain in its extended position during movement of a roadbuilding machine on which said fork is mounted.

9. A support for a grade-wire comprising: a plurality of stakes and awire hanger having one end thereof adjustably connected to each of saidstakes, the other end of said wire hanger including a verticallyextending fork spreading plate having a diagonally positioned slotextending therethrough and into said wire hanger, said slot singdimensioned for grade-wire receivement and portions thereof on said wirehanger being conditioned to retain and support a grade-wire, thevertical dimension of said fork spreading plate lying between two smoothconcavely opposed and intersecting surfaces and gradually decreasingfrom its center position to its points of intersection in a common planecontaining said slot portions.

10. in combination with an earth working vehicle having control meansfor varying the position of an earth working tool thereon transverse toa surface being worked in relation to disposition of a grade wire, asurface detecting and controlling assembly comprising:

a fork assembly extending from said vehicle and pivotally mountedthereon for oscillatory movement in a plane transverse to a surfacebeing worked thereby,

means operating said control means in response to said oscillatorymovement,

said fork assembly including a pair of prongs spreadable in saidtransverse plane,

a plurality of wire hangers,

a grade wire retaining slot in each of said wire hangers,

said prongs being adapted to engage said grade wire and move therealongwith said vehicle,

mounting means for supporting said wire hangers with said retaining slotat a selected distance from the surface being worked,

each of said wire hangers including a fork spreading member including apair of opposed surfaces diverging vertically in the direction ofvehicle travel from points within boundaries defined by the upper andlower surfaces of a retained grade wire.

11. The combination defined in claim 10 including:

a second pivotal mounting on said vehicle supporting said fork assemblyfor oscillatory movement in a plane parallel to said surface beingworked, and

yieldable means urging said fork assembly into a centered position aboutsaid second pivotal mounting generally perpendicular to the direction ofvehicle movement.

12. In combination with an earth working vehicle having control meansfor varying the elevation of an earth working tool thereon, a surfacedetecting and controlling assembly comprising:

a fork assembly extending from said vehicle and pivot ally mountedthereon for oscillatory movements in a plane perpendicular to thedirection of vehicle travel,

means for operating said control means in response to said oscillatorymovements,

a pair of prongs on the free end of said fork assembly spreadable insaid perpendicular plane,

a plurality of wire hangers,

a grade-wire retaining slot in each of said wire hangers,

said prongs being adapted to engage said grade-wire and move therealongwith said vehicle,

mounting means for supporting said wire hangers with said retaining slotat a selected elevation above a surface being worked, and

a fork spreader on each of said wire hangers having a pair of surfacesdiverging in the direction of vehicle travel,

said surfaces intersecting in a plane containing said retaining slot.

13. The combination defined in claim 12 including:

a second pivotal mounting on said vehicle supporting said fork assemblyfor oscillatory movement in a plane parallel to the direction of vehicletravel, and

yieldable means urging said fork assembly into a centered position aboutsaid second pivotal mounting generally perpendicular to the direction ofvehicle movement,

said yieldable means being strong enough to resist movement of said forkassembly in said parallel plane upon engagement thereof with a forkspreader to cause said prongs to spread and pass thereover and resumeengagement with said grade-wire.

14. The combination defined in claim 12 including:

yieldable means urging said fork assembly upward in said perpendicularplane to counterbalance the effect of gravity thereon so that saidgrade-wire need not support said fork assembly as it moves therealong.

till 15. A wire fork assembly for controlling the tool elevation of anearth working vehicle in accordance with a ground supported grade-wireextending alon the path of movement of said vehicle, said wire forkassembly comprising:

a control member rotatably mounted on said road building machine forlimited angular displacement about an axis parallel to the path ofvehicle movement,

said control member being operative to actuate control means foradjusting said tool elevation in response to the angular position ofsaid control member about said parallel axis;

a fork assembly mounted on said control member to rotate therewith,

said fork assembly extending laterally from said vehicle and terminatingin a pair of prongs operative to engage a grade-wire;

a swivel connection in said fork assembly to permit said prongs to moveabout a vertical axis; and

a closely wound extension coil spring secured across said swivelconnection for normally centering said fork assembly about said verticalaxis and in lateral extension.

References Cited by the Examiner UNITED STATES PATENTS 541,019 6/95Smith 191-43 568,452 9/96 McCallurn 191-43 2,864,452 12/58 Guntert eta1. 2,902,908 9/59 Schiavi 9439 2,922,345 l/ Mentes.

JACOB L. NACKENOFF, Primary Examiner.

4. A WIRE FORK ASSEMBLY FOR CONTROLLING THE VERTICAL TOOL HEIGHT OF AROAD BUILDING MACHINE IN ACCORDANCE WITH A GROUND SUPPORTED GRADE-WIREEXTENDING ALONG THE PATH OF MOVEMENT OF SAID ROAD BUILDING MACHINE, SAIDWIRE FORK ASSEMBLY COMPRISING: A CONTROL MEMBER ROTATABLY MOUNTED TOSAID ROAD BUILDING MACHINE FOR LIMITED ANGULAR DISPLACEMENT ABOUT ANAXIS PARALLEL TO SAID GRADE WIRE, SAID CONTROL MEMBER BEING OPERATIVE TOACTUATE CONTROL MEANS FOR SELECTIVELY RAISING AND LOWERING SAID VERTICALTOOL HEIGHT IN RESPONSE TO AN ANGULAR POSITION ABOUT SAID AXIS; A SLEEVESUPPORT MOUNTED TO SAID CONTROL SHAFT, A HORIZONTALLY EXTENDING SLEEVESWIVELY CONNECTED TO SAID SLEEVE SUPPORT FOR SWIVELING ABOUT A VERTICALAXIS; A CLOSELY WOUND EXTENSION COIL SPRING CONNECTED BETWEEN SAIDSLEEVE SUPPORT AND SAID SLEEVE FOR NORMALLY CENTERING SAID SLEEVE ABOUTAN AXIS PERPENDICULAR TO SAID CONTROL MEMBER; AND A WIRE FORK SUPPORTEDBY SAID SLEEVE AND OPERATIVE TO ENGAGE SAID GRADE WIRE.